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Bedding a steel fitting on the hull, a drogue question

Fascadale

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I have assembled a Jordan Series Drogue. There are more details here.

I now have to work out the details of the attachment system. Don Jordan recommended.............

..........................“The optimum attachment for the drogue is clearly a strap similar to a chain plate, bolted to the hull at the corners of the transom as shown in the sketch. This arrangement feeds the load directly into the hull and imposes no bending or pullout loads on the hull or deck. For a load of 14,000 lbs a strap 1⁄4 x 2.25 x 18 inches attached by six 3/8 inch bolts would provide a conservative design.”

To this end I have had fabricated two stainless steel straps, about 4.5mm by 60mm by 18 inchs. These will be held on with four or perhaps three countersunk M10 machine screws through bolted with suitable backing plates. (I sail a heavily built long keeled 26ft MAB, displ. 5,130 lbs plus kit)

My question concerns bedding the straps to the hull. They will be mounted on a virtually flat area just below the toerail.

Should I put anything between the strap and the hull and if so what? Something which will set solid or something that will retain some flexibility? Recommendations please.

I suppose the same question applies to the backing plates.

Thanks
 

vyv_cox

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If you bolt directly to the hull the straps and bolts will suffer from crevice corrosion. Bed them on a suitable mastic, which for me would be Sikaflex 291.
 

Frankie-H

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I have always believed that this argument is seriously flawed.

I have tried both ways and seriously believe that I would rather lie bows to heavy weather, when you feel it necessary to lie to a drogue.

If you are in danger of overreaching and need to slow the boat down, then warps or indeed your drogue from the stern will still allow you some steerage way. If, however, the weather is bad enough to lie hove to, then I would prefer the safety of having my bows into the weather. Bows are designed to have water break over them and most of it will carry away. Sterns are not. Slow the boat down by the stern in this sort of weather and you will be in severe danger of getting pooped.

I would prefer to use my deck cleats, which have been designed to take the snatch loads of the boat. Both fwd and aft depending on the conditions.

Also give thought to recovery. You will never pull in your drogue by hand, unless the boat is completely stationary and even being pulled back to the drogue. You will need to use your winches to recover. I assume that the drogue has a line from the far end, so that you can release the tow and collapse the series.
 

Fascadale

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I have always believed that this argument is seriously flawed.

I have tried both ways and seriously believe that I would rather lie bows to heavy weather, when you feel it necessary to lie to a drogue.

If you are in danger of overreaching and need to slow the boat down, then warps or indeed your drogue from the stern will still allow you some steerage way. If, however, the weather is bad enough to lie hove to, then I would prefer the safety of having my bows into the weather. Bows are designed to have water break over them and most of it will carry away. Sterns are not. Slow the boat down by the stern in this sort of weather and you will be in severe danger of getting pooped.

I would prefer to use my deck cleats, which have been designed to take the snatch loads of the boat. Both fwd and aft depending on the conditions.

Also give thought to recovery. You will never pull in your drogue by hand, unless the boat is completely stationary and even being pulled back to the drogue. You will need to use your winches to recover. I assume that the drogue has a line from the far end, so that you can release the tow and collapse the series.

Thank you for your comments, but as I said I have assembled a JSD and am looking for advice on a specific technical issue.

Should you wish a more general discussion of drogues, sea brakes, bow on, stern on, the Pardy method and other questions then perhaps this is the thread for you. There is also another JSD discussion here where drogue discovery is discussed

Thank you again for your comments.
 
Joined
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West country
I'm looking to fit something rather similar....


...because I have them.

Titanium. Harken. 92mm across, with 10mm x 10mm min cross-section. I intend to use 12mm s/s bolts and nuts 'cos they're available. Is crevice corrosion still an issue, or should I source bronze.

I fear that 8 x 1/2inch titanium bolts 'n nuts from Harken might cost more than the boat...

Anyway, the rode is/will be not more than 14mm braid-on-braid and should certainly 'let go' before bits of the hull pull off.

Same Sikaflex bedding?
 

vyv_cox

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Lovely looking kit! I would use 316 (A4) stainless bolts and nuts, or 304 (A2) nuts would be OK below deck. Provided the bolts are bedded in the Sikaflex around the countersinks I doubt that corrosion will be a problem.
 

Talbot

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I would expect at least 5 bolts for each strap. I intend to bed mine on sikkaflex.

Have you considered>

1. Is the deck solid - if cored, you will need to remove some core and fill with epoxy.

2. Is the deck strong enough to take the load. - I plan to add sufficient matting to spread the load, and ensure that the plate cannot pull through the deck.


If you work on the concept that these straps should be strong enough to be able to take the weight of the boat, if the boat could be tipped up 90 deg on its nose and then lifted by a crane.
 

Tranona

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I would expect at least 5 bolts for each strap. I intend to bed mine on sikkaflex.

Have you considered>

1. Is the deck solid - if cored, you will need to remove some core and fill with epoxy.

2. Is the deck strong enough to take the load. - I plan to add sufficient matting to spread the load, and ensure that the plate cannot pull through the deck.


If you work on the concept that these straps should be strong enough to be able to take the weight of the boat, if the boat could be tipped up 90 deg on its nose and then lifted by a crane.
The OP is bolting through the transom, not the deck. Don't think there is any issue about strength of the fittings or fastenings, just about whether they should be bedded with a sealant - to which the answer is Yes.
 

prv

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The OP is bolting through the transom, not the deck. Don't think there is any issue about strength of the fittings or fastenings, just about whether they should be bedded with a sealant - to which the answer is Yes.
Actually I think he's mounting them on the topsides, at the aft end with presumably the end of the strap protruding past the transom. Seems like a good solid mounting to me; faced with the same requirement I would do much the same. I would certainly bed them on Sikaflex 291.

Pete
 

Tranona

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Yes, see that now. The fastenings will be in tension then, so should be pretty secure. Potentially a "wet" location at times so good sealant needed.
 

vyv_cox

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I have used butyl tape for bedding windows, at which it is superb. However, being non-setting it goes on extruding almost indefinitely, which is not a property I would want in a heavily bolted and loaded fitting. I would go with the Sikaflex 291.
 

Fascadale

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Actually I think he's mounting them on the topsides, at the aft end with presumably the end of the strap protruding past the transom. Seems like a good solid mounting to me; faced with the same requirement I would do much the same. I would certainly bed them on Sikaflex 291.

Pete
Correct

I have used butyl tape for bedding windows, at which it is superb. However, being non-setting it goes on extruding almost indefinitely, which is not a property I would want in a heavily bolted and loaded fitting. I would go with the Sikaflex 291.

Does Sikaflex 291 go solid or does it retain an element of flexibility?

Would you recommend the same treatment for the backing plates ?

(I plan to use a length of lighter grade stainless for the backing plates, the sort of stuff they fabricate industrial kitchen splashbacks)
 

vyv_cox

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Does Sikaflex 291 go solid or does it retain an element of flexibility?

Would you recommend the same treatment for the backing plates ?

(I plan to use a length of lighter grade stainless for the backing plates, the sort of stuff they fabricate industrial kitchen splashbacks)
Some flexibility. Even old stuff that has been in place for years is quite elastic after peeling off fittings. It is widely used for chain plates, for example, which seems to be a similar duty.

I can't see a lot of value in using it for backing plates provided they are a good fit to the hull. I probably would though, as an extra precaution and to avoid staining.
 

Fascadale

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Some flexibility. Even old stuff that has been in place for years is quite elastic after peeling off fittings. It is widely used for chain plates, for example, which seems to be a similar duty.

I can't see a lot of value in using it for backing plates provided they are a good fit to the hull. I probably would though, as an extra precaution and to avoid staining.
Thanks for that
 

Tranona

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Correct




Does Sikaflex 291 go solid or does it retain an element of flexibility?

Would you recommend the same treatment for the backing plates ?

(I plan to use a length of lighter grade stainless for the backing plates, the sort of stuff they fabricate industrial kitchen splashbacks)
Not sure why you are worried about flexibility. It is not going to move once you have bolted it down. The sealant is to stop water from getting in and also to seal the threads to prevent crevice corrosion.
 

Twister_Ken

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'ang on a mo, I'll just take some bearings
I like the sound of the set-up proposed, but worry slightly about how practical it would be to rig the drogue with plates in that position when - presumably you're running downwind in a big sea, maybe rolling the gunwales under. Wouldn't a location a bit further inboard be better?
 

prv

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I like the sound of the set-up proposed, but worry slightly about how practical it would be to rig the drogue with plates in that position when - presumably you're running downwind in a big sea, maybe rolling the gunwales under. Wouldn't a location a bit further inboard be better?
Hard to see how to mount the anchors further inboard without sacrificing strength. Probably better off with a pendant attached and led inboard ready for use, if it's hard to get at the plates. Although really, just below the toe-rails on the quarters shouldn't be too hard, surely?

Pete
 
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